The present invention relates to a control system for a material handling device and more particularly to a control system of the type in which additional power required for a first motion, such as hoisting, may be obtained from the power source for a second motion such as drag and conversely additional power for the second motion may be obtained from the power available for the first motion under specified conditions.
Material handling apparatus, for example, a drag line, have a material handling device such as a bucket or scoop suspended from an inclined boom by means of a first cable. In such case, the bucket is designed such that when it is pulled toward the base of the boom by a second cable, it will scrape soil or other material from the surface being excavated. The first and second cables are normally wound upon motor driven reels such that rotation of the respective reels in one direction or the other will determine the position of the bucket and its direction of movement. Completely independent hoist and drag machinery is used for these operations including the electrical system. In addition, a third motion, such as swing, may be used to rotate the upper portion of the apparatus with respect to its base. This motion also requires separate machinery. Thus, at least one driving motor is used for each motion of the material handling device such as the bucket of a dragline excavator. For instance, one or more electric motors are used to hoist the bucket and one or more separate electric motors are used to drag the bucket in a horizontal plane and one or more separate electric motors are used to rotate the upper portion of the apparatus. For each driving motor a separate generator is used and the generators are driven by one or more AC motors. No attempt is made to switch the generators from one motion motor to another motion motor. This is done because the current flow interruption through existing electrical knife blades, contacters and the like would cause tremendous arcing problems.
However, once the material handling apparatus or device is constructed, it is almost impossible to add an additional motor to add greater power in one or more of the motions because there must also be added to the system an additional generator and an AC motor to drive the generator. Even if space were available to add the extra DC motor, the DC generator and the AC motor to drive the generator, the approach would be very expensive.
The present invention relates to an electronic switching system which automatically diverts the power output from one DC generator powering a DC motor for one motion to drive a supplementary DC motor used in powering the other motion. For simplicity in explanation, drag and hoist motions will be discussed but it should be understood that the novel invention can be used with other motions such as crawl, swing, and the like. If it is recognized that during a first motion, the power in a second motion is very low, the availability of using a generator from the second motion to drive a motor for the first motion is present by using one of the second motion generators. The generator is switched to the other motion only when the power requirement for the former motion is at a minimum. As an example only, drag motion power requirement is at a minimum during the hoisting motion. A DC generator output used to drive the drag motion DC motor is switched electronically by the present invention to drive a supplementary hoisting motion DC motor. The switching process is accomplished by utilizing switches such as silicon controlled rectifiers which can handle the output current of the generator.
Thus, it is recognized that the duty cycle of each motion is not the same and that a generator can be "borrowed" from one motion to drive an added motor necessary to assist in the other motion.
It is therefore an object of the present invention to "borrow" additional power from an existing generator powering a motor controlling a first motion to drive an added motor assisting the motors controlling a second motion.
It is also an object of the present invention to provide power for additional DC motors without adding additional DC generators and additional AC motors.
It is still another object of the present invention to utilize the existing DC generators in providing power for a first motion to be switched to an additional DC motor for a second motion when the duty cycle of the first motion is low.